Showing papers by "Iowa State University published in 1991"

The continuation power flow: a tool for steady state voltage stability analysis

Abstract: The authors present a method of finding a continuum of power flow solutions starting at some base load and leading to the steady-state voltage stability limit (critical point) of the system. A salient feature of the so-called continuation power flow is that it remains well-conditioned at and around the critical point. As a consequence, divergence due to ill-conditioning is not encountered at the critical point, even when single-precision computation is used. Intermediate results of the process are used to develop a voltage stability index and identify areas of the system most prone to voltage collapse. Examples are given where the voltage stability of a system is analyzed using several different scenarios of load increase. >

Selves in Transition: Symbolic Consumption in Personal Rites of Passage and Identity Reconstruction

Abstract: The consumption of aesthetic plastic surgery is examined within the broader context of daily life in an investigation of the motives and the self-concept dynamics underlying this symbolic consumer behavior. Data were collected in multiple, in-depth, ethnographic interviews, and analyzed by a constant comparative method revealing insights into both a priori and emergent themes. A priori themes regarding body image, impression management, symbolic self-completion, and possible selves are developed through a literature review and discussed briefly in light of the findings. Emergent themes, including role transitions, sexual selves and romantic fantasies, control and efficacy, and identity play are developed and embedded in a discussion of identity reconstruction and personal rites of passage. It is concluded that consumption activities are important to both the maintenance and the development of a stable, harmonious self-concept. Directions for future research are discussed.

Systemic Endopolyploidy in Arabidopsis thaliana

Abstract: Microfluorometric analysis of the nuclear DNA contents of the somatic tissues of Arabidopsis thaliana has revealed extensive endoreduplication, resulting in tissues that comprise mixtures of polyploid cells. Endoreduplication was found in all tissues except those of the inflorescences and was developmentally regulated according to the age of the tissues and their position within the plant.

Unified theory of effects of vortex pinning and flux creep upon the rf surface impedance of type-II superconductors.

Abstract: We present a new theoretical approach that permits the rf surface impedance ${\mathit{Z}}_{\mathit{s}}$ of type-II superconductors to be calculated over a wide range of angular frequencies \ensuremath{\omega}, magnetic inductions B, and temperatures T. Our approach, based on a self-consistent treatment of vortex dynamics, includes the influence of both vortex pinning and flux creep upon ${\mathit{Z}}_{\mathit{s}}$ in a unified manner, by making use of continued-fraction-expansion results for the dynamic mobility of a particle undergoing Brownian motion in a periodic potential.

Scanning tunneling microscopy of ethanethiolate and n-octadecanethiolate monolayers spontaneously adsorbed at gold surfaces

Abstract: Monolayer films from ethanethiol (ET) and n-octadecanethiol (OT) spontaneously adsorbed onto epitaxially grown Au(111) films on mica were examined by scanning tunneling microscopy (STM). The resulting atomically resolved images are the first reported for gold-adsorbed organothiolate molecules and reveal the packing arrangement of the overlayer. Tunneling is presumed to occur between the microscope tip and the gold-bound sulfur of the n-alkanethiolate head group. For both the ET and QT monolayers, an image that corresponds to a hxagonally packed array of adsorbates with respective nearest-neighbor and next-neighbor spacings of 0.50±0.02 and 0.87±0.04 nm was observed

Structure and interfacial properties of spontaneously adsorbed n-alkanethiolate monolayers on evaporated silver surfaces

Abstract: Monolayer films of n-alkanethiols (CH 3 (CH 2 ) n SH, n=3-15, 17) have been spontaneously adsorbed from solution at evaporated Ag films. These monolayers have been characterized with optical ellipsometry, contact angle measurements, and external reflection infrared spectroscopy (IRS). The IRS data indicate that the monolayers with long chains (n≥10) are predominantly densely packed, crystalline-like structures with all-trans conformational sequences exhibiting average tilts of ∼13 o from the surface normal

Single transverse spin asymmetries.

Abstract: Using generalized factorization theorems, we calculate the leading single transverse spin asymmetry for high transverse-momentum direct-photon production in pp collisions, in terms of partonic matrix elements. The leading contribution comes from a ``twist-3'' parton distribution, involving the correlation between quark fields and the gluonic field strength. With simple assumptions for this matrix element, the asymmetry increases with ${\mathit{x}}_{\mathit{F}}$, naturally giving effects of 10% or more at large ${\mathit{x}}_{\mathit{F}}$.

Causality between transnational terrorism and tourism: The case of Spain

Abstract: The purpose of this paper is to devise a methodology for estimating the impact of transnational terrorism on tourism. Using monthly data from 1970–1988, we estimate the relationship between terrorism and tourism for Spain. We find that terrorist events have had a significant negative impact on the number of tourists visiting Spain. A typical incident is estimated as scaring away just over 140,000 tourists when all monthly impacts are combined. Moreover, the causality is unidirectional: terrorism affects tourism, but not the reverse.

Intergenerational transmission of harsh parenting.

Abstract: A social learning model was developed that portrayed four processes whereby harsh parenting might be transmitted across generations. The model was tested using a sample of 451 2-parent families, each of which included a 7th grader. Both parent self-report and adolescent-report measures were utilized for the harsh parenting construct.

Bifurcation theory and its application to nonlinear dynamical phenomena in an electrical power system

Abstract: A tutorial introduction in bifurcation theory is given, and the applicability of this theory to study nonlinear dynamical phenomena in a power system network is explored. The predicted behavior is verified through time simulation. Systematic application of the theory revealed the existence of stable and unstable periodic solutions as well as voltage collapse. A particular response depends on the value of the parameter under consideration. It is shown that voltage collapse is a subset of the overall bifurcation phenomena that a system may experience under the influence of system parameters. A low-dimensional center manifold reduction is applied to capture the relevant dynamics involved in the voltage collapse process. The need for the consideration of nonlinearity, especially when the system is highly stressed, is emphasized. >

Biodegradation of degradable plastic polyethylene by phanerochaete and streptomyces species.

Abstract: The ability of lignin-degrading microorganisms to attack degradable plastics was investigated in pure shake flask culture studies. The degradable plastic used in this study was produced commercially by using the Archer-Daniels-Midland POLYCLEAN masterbatch and contained pro-oxidant and 6% starch. The known lignin-degrading bacteria Streptomyces viridosporus T7A, S. badius 252, and S. setonii 75Vi2 and fungus Phanerochaete chrysosporium were used. Pro-oxidant activity was accelerated by placing a sheet of plastic into a drying oven at 70 degrees C under atmospheric pressure and air for 0, 4, 8, 12, 16, or 20 days. The effect of 2-, 4-, and 8-week longwave UV irradiation at 365 nm on plastic biodegradability was also investigated. For shake flask cultures, plastics were chemically disinfected and incubated-shaken at 125 rpm at 37 degrees C in 0.6% yeast extract medium (pH 7.1) for Streptomyces spp. and at 30 degrees C for the fungus in 3% malt extract medium (pH 4.5) for 4 weeks along with an uninoculated control for each treatment. Weight loss data were inconclusive because of cell mass accumulation. For almost every 70 degrees C heat-treated film, the Streptomyces spp. demonstrated a further reduction in percent elongation and polyethylene molecular weight average when compared with the corresponding uninoculated control. Significant (P < 0.05) reductions were demonstrated for the 4- and 8-day heat-treated films by all three bacteria. Heat-treated films incubated with P. chrysosporium consistently demonstrated higher percent elongation and molecular weight average than the corresponding uninoculated controls, but were lower than the corresponding zero controls (heat-treated films without 4-week incubation). The 2- and 4-week UV-treated films showed the greatest biodegradation by all three bacteria. Virtually no degradation by the fungus was observed. To our knowledge, this is the first report demonstrating bacterial degradation of these oxidized polyethylenes in pure culture.

Suppression of Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae) by Endophytic Beauveria bassiana (Balsamo) Vuillemin

Abstract: The ubiquitous entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin was applied to whorl-stage corn plants, Zea mays L., by foliar application of a granular formulation of conidia and by injection of a conidial suspension. Plants were analyzed at harvest for presence of B. bassiana and for the amount of tunneling by laboratory-reared European corn borer larvae, Ostrinia nubilalis (Hubner). In 1989, 98.3% of the foliarly treated plants, 95.0% of the injected plants, and 33.3% of the nontreated plants were colonized by B. bassiana at harvest. In 1988, there were no significant differences between treatment effects on O. nubilalis tunneling in plants. In 1989, when environmental conditions were more conducive to fungal growth, tunneling was significantly greater in the control plants, followed by the injected and foliarly treated plants. When applied to foliage, B. bassiana provided the greatest amount of O. nubilalis suppression. The entomopathogenic fungus colonized the corn plant at whorl stage, moved within the plant, and persisted to provide season-long suppression of O. nubilalis .

Sexual Abuse as a Precursor to Prostitution and Victimization Among Adolescent and Adult Homeless Women

Abstract: Previous research indicates that women who were sexually abused as children are more likely to become involved in prostitution and to experience criminal victimization. A sample of 40 adolescent runaways and a sample of 95 homeless women were studied to test direct and indirect models of the impact of early sexual abuse on prostitution and victimization. The results suggest that early sexual abuse increases the probability of involvement in prostitution irrespective of any influence exerted through factors such as running away from home, substance abuse, and other deviant activities. In contrast, the findings indicate that early sexual abuse only indirectly affects the chances of victimization by increasing the likelihood of a life-style based on participation in risky activities and events.

Genetic improvement of maize yields.

Abstract: Publisher Summary Grain yields for maize are expected to increase because of the combined effects of two items—improved cultural practices and management and increased genetic potential of the hybrids. The improvements of these items can be expected to contribute significantly to give higher state averages in the future. An important cause for yield gain is that the genetic potential of the most recent hybrids takes advantage of higher plant densities to produce more grain per unit field area. Perhaps further gains can be achieved by the development and evaluation of parental materials at higher plant densities to identify greater resistance to barrenness. Stalk lodging, however, is still a major problem and must be corrected if higher plant densities are to be used. Consequently, breeders must develop materials that have better disease resistance and stalk quality before hybrids can be planted at higher plant densities to produce more grain per unit area. Recurrent selection can be used effectively to improve stalk quality in breeding populations, but caution must be used in selection to avoid yield declines. Occasionally, germplasm with resistance for some pests may have to be introduced from unadapted sources, and this could cause temporary reductions for hybrid performance until unfavorable genes linked with the resistance genes are eliminated.

Transition temperatures of superconductor-ferromagnet superlattices

Abstract: The transition temperature ${\mathit{T}}_{\mathit{c}}$ of superconductor-ferromagnet superlattices is calculated by solving exactly the Usadel equations. Characteristic ground-state configurations are predicted with nontrivial phase difference 0cphi\ensuremath{\le}\ensuremath{\pi} between neighboring superconducting layers. An unusual oscillatory dependence of ${\mathit{T}}_{\mathit{c}}$ on the ferromagnetic-layer thickness is obtained. For short-period superlattices it is found that the transition changes from second to first order. A comparison of theoretical results with experimental data for V/Fe superlattices is given.

Asteroseismology of the DOV star PG 1159 - 035 with the Whole Earth Telescope

Abstract: Results are reported from 264.1 hr of nearly continuous time-series photometry on the pulsating prewhite dwarf star (DPV) PG 1159 - 035. The power spectrum of the data set is completely resolved into 125 individual frequencies; 101 of them are identified with specific quantized pulsation modes, and the rest are completely consistent with such modal assignment. It is argued that the luminosity variations are certainly the result of g-mode pulsations. Although the amplitudes of some of the peaks exhibit significant variations on the time scales of a year or so, the underlying frequency structure of the pulsations is stable over much longer intervals. The existing linear theory is invoked to determine, or strongly constrain, many of the fundamental physical parameters describing this star. Its mass is found to be 0.586 solar mass, is rotation period 1.38 days, its magnetic field less than 6000 G, its pulsation and rotation axes to be aligned, and its outer layers to be compositionally stratified.

Applying Latent Trait Analysis in the Evaluation of Prospects For Cross-Selling of Financial Services

Abstract: Identification of the order in which households acquire financial services has important implications for market seg­mentation and cross-selling strategies. This study illustrates a procedure by which financial institutions, based on internal records can estimate the likelihood that a customer will purchase/use additional services. The methodology discussed in this study positions financial services and investors along the same continuum according to the particular ownership pattern. The location of an investor indicates his financial expertise and resources, while the location of a financial service measures the level of expertise/resources needed for ownership of that service.A key feature of the methodology is its ability to predict the probability of ownership of some financial services given information on (non-)ownership of other services. This study concludes with an illustration applying the methodology for targeting customers for cross-selling efforts.

Ionic Conduction in Phosphate Glasses

Abstract: Ionic conductivity in phosphate glasses has been known for almost 30 years. Recently these glasses have been shown to exhibit some of the highest ionic conductivities ever reported. In many cases, because of their ease of preparation, low melting points, strong glass-forming character, and simple composition, phosphate glasses have been studied more than any other ionically conducting glasses. However, no single review has ever been made of these glasses with the purpose of correlating the apparent widely disparate values of conductivity that these glasses exhibit. In this review, the conductivities of phosphate glasses are examined considering new structural studies of them. A systematic comparison of the dependence of the conductivity on glass chemistry reveals that, similar to other glass families (silicates and borates for example), the conductivity maximizes when the cation environments in the glass are minimized in their charge density and maximized in their site proximity.

Concentrations of fumonisin B1 in feeds associated with animal health problems

Abstract: Ninety-eight samples of feeds associated with 44 cases of equine leukoencephalomalacia (ELEM) and 83 samples of feed associated with 42 cases of a porcine pulmonary edema syndrome (PPE) were analyzed for fumonisin B1 (FB1). For comparison purposes, 51 feed samples not associated with PPE or ELEM were also analyzed. Feed associated with ELEM contained FB1 ranging from less than 1 microgram/g to 126 micrograms/g with 75% of the cases having at least 1 sample above 10 micrograms/g. Feeds associated with PPE ranged from less than 1 microgram/g to 330 micrograms/g with 71% of the cases having at least 1 sample greater than 10 micrograms/g. Quantitation was by high performance liquid chromatography (HPLC)/fluorescence using the fluorescamine derivative with confirmation by thin layer chromatography (TLC) and/or gas chromatography/mass spectroscopy (GC/MS).

Parenting factors, social skills, and value commitments as precursors to school failure, involvement with deviant peers, and delinquent behavior

Abstract: Elements of social control theory were combined with social learning theory to construct a model of delinquency which specifies the manner in which parenting factors, social skills, value commitments, and problems in school contribute to association with deviant peers and involvement in delinquent behavior. The model was tested using a sample of 61 families, each of which included a seventh grader. Questionnaire responses and coded videotaped family interaction were employed as measures of study constructs. The results largely supported the proposed model.

Application of surface-enhanced Raman spectroscopy to biological systems

Abstract: This review summarizes the literature relating to the application of surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) techniques to the study of biological molecules. The emphasis is on publications that have appeared during the period from 1985 to 1991. The review is divided into six major parts. First, a brief overview of the current understanding of the mechanistic aspects of SERS/SERRS is given, with an emphasis on the relationship between theoretical predictions and experimental results. The most common experimental systems (colloids, metal island films, and electrodes) are described. Studies of biological systems are described in the second (small molecules), third (DNA and proteins) and fourth (membranes proteins and membrane preparations) sections. In the fifth or conclusion section, the potential use of SERS or SERRS as a method for obtaining spectra of native biological molecules is evaluated. Finally, the sixth section describes advances in Raman instrumentation in terms of their possible impact on future applications of SERS/SERRS techniques to biological molecules.

Eyewitness identification and the selection of distracters for lineups

Abstract: Previous treatments of eyewitness lineups have focused exclusively on the importance of homogeneity (similarity of common features) in the physical characteristics of lineup members. This has led to some confusion about the proper way to select distracters. We argue that distracters should not be selected for their similarity to the suspect but rather for their similarity to the witness's description of the culprit. The similarity-to-suspect strategy fails to define limits to the number, type, and degree of featureal matching and falls prey to the logical extension that a good lineup is composed of the suspect's clones. Accordingly, the similarity-to-suspect strategy has no supportive logic in recognition memory theory and gives no credit to the importance of hit rates. The similarity-to-witness's-description-of-culprit criterion, on the other hand, specifies a finite and manageable set of feature requirements for distracters, articulates a role for heterogeneous features, meets all functional requirements for fairness to the suspect, has a supportive logic in recognition memory theory, preserves hit rates, and is not subject to the clone argument.

Parentage determination in maize hybrids using the arbitrarily primed polymerase chain reaction (AP-PCR).

Abstract: Using a novel procedure based on the polymerase chain reaction, we have developed a rapid, efficient, and economical method for identifying plant genotypes. The arbitrarily primed polymerase chain reaction (AP-PCR) generates reproducible fingerprints from any organism, without the need for DNA sequence information. These fingerprints include DNA fragment polymorphisms that can be (1) used for varietal identification and parentage determination, (2) followed in segregating populations produced by crosses, (3) used as markers for the construction of genetic maps, and (4) used to generate dendograms of phylogenetic relationships, especially at the intraspecific level. AP-PCR requires only minute quantities of DNA (10–25 ng per reaction) and therefore can be used in situations in which DNA is limiting. We demonstrate the use of AP-PCR to identify inbred parents of hybrid maize plants in double-blind experiments.

Modular specification and verification of object-oriented programs

Abstract: A method for modular specification and verification using the ideas of subtype and normal type is presented. The method corresponds to informal techniques used by object-oriented programmers. The key idea is that objects of a subtype must behave like objects of that type's supertypes. An example program is used to show the reasoning problems that supertype abstraction may cause and how the method resolves them. Subtype polymorphism is addressed, and specification and verification update is discussed. A set of syntactic and semantic constraints on subtype relationships, which formalize the intuition that each object of a subtype must behave like some object of each of its supertypes, is examined. These constraints are the key to the soundness of the method. To state them precisely, a formal model of abstract type specifications is used. >